The present invention relates to an ink reservoir for providing a supply of pressurized ink to a printer. More particularly, the present invention relates to a method and apparatus for biasing a flexible ink reservoir to provide a supply of ink at constant pressure to the printer.
Printers typically include a drop ejection device and a supply of ink for replenishing the drop ejection device. In the case of thermal printing, the drop ejection device is typically referred to as a printhead. Printing is accomplished by the selective activation of the printhead as the printhead is moved relative to a print media.
One previously used type of printer makes use of an ink reservoir that is separately replaceable from the printhead. As ink is selectively deposited on print media, the ink reservoir replenishes the printhead with ink. In this embodiment, a region within the printhead is maintained at a slight vacuum, sometimes referred to as xe2x80x9cbackpressure.xe2x80x9d Typically, this backpressure is approximately two to three inches of water below atmospheric pressure. This backpressure within the printhead tends to prevent ink from leaking or drooling from nozzles within the printhead which can reduce print quality. If this backpressure is too large, ink flow to ink ejection chambers is reduced. This is sometimes referred to as xe2x80x9cprinthead starvationxe2x80x9d resulting in print quality degradation and possible printhead failure.
The replaceable ink reservoir can be positioned on a scanning carriage with the printhead or positioned off the scanning carriage. In the case where the ink reservoir is mounted off carriage, the ink reservoir can be continuously in fluid communication with the printhead such as connected by a flexible conduit or intermittently connected by positioning the carriage proximate a refilling station that is in fluid communication with the printhead. The printhead is selectively replenished with ink from the refilling station. Using a replaceable ink reservoir allows for the replacement of the ink reservoir separate from the printhead allowing the use of the printhead until end of printhead life thereby reducing the cost per page of printing to the consumer.
It is frequently useful for providing a pressurized supply of ink to the printhead to achieve high flow rates or greater reliability. High flow rates are sometimes required in large format printing. Large format printing often involves printing on print media on the order of 34-54 inches in width. High flow rates are required in small format printing in cases where high print speed is required.
Various schemes have been suggested for pressurizing sources of ink. U.S. Pat. No. 5,650,811 entitled xe2x80x9cApparatus for Providing Ink to a Printheadxe2x80x9d, issued Jul. 22, 1997, to Seccombe et al., discloses the use of a spring for urging a piston to engage a deformable bag filled with ink.
There is an ever-present need for techniques for providing a pressurized supply of ink to achieve high flow rates and high reliability. These techniques should minimize pressure variations thereby reducing the pressure range in which the pressure regulator must compensate. In addition, these techniques should be volumetrically efficient to provide a compact ink reservoir, well suited to high volume manufacturing and be relatively low cost thereby reducing the per page print costs.
These techniques should be capable of dispensing substantially all of the ink from the replaceable ink reservoir. Stranding ink in the replaceable ink reservoir tends to reduce the consumer value. In addition, stranded ink within the replaceable ink container produces an added component in the waste stream when the ink container is discarded.
Finally, these techniques for producing a pressurized supply of ink should allow for the determination of remaining ink in the ink reservoir. It is important that the remaining ink in the ink reservoir be capable of accurately being measured to provide advance notice that the ink reservoir is in need of replacement. Another important reason for determining an amount of remaining ink in the ink reservoir is to prevent operation of the printer when the ink reservoir is exhausted of ink. In the case of thermal printers, operation of the printhead without an adequate supply of ink can result in catastrophic damage to the printhead.
The present invention is a constant pressure ink supply for use in a printing system. The ink supply includes a flexible fluid reservoir for containing a quantity of fluid, and a spring which has an expanded position, and a contracted position. The spring is configured to operatively engage the flexible ink reservoir as the spring transitions from the expanded position to the contracted position and wherein the flexible fluid reservoir is biased by the spring as the spring contracts to produce fluid at a substantially constant fluid pressure at a fluid outlet.